Process of converting acetylenic hydrocarbons to aromatic hydrocarbons



I Patented Oct. 8, 1940 A UNITED STATES PROCESS OF CONVERTING AGE'I'YLENIC HYDROOARBONS T0 AROMATIC CABBONS Arlstid V. Grease and William J. Mattox, Chicago, 111., assignors to Universal Oil Products Company, Chicago, 111., a corporation of Delaware No Drawing. Application May 31, 1938,

Serial No. 211,020

6 Claims. I (c1. zoo-sea) tion by the present types of catalysts, the follow- This invention relates more particularlyto the conversion of straight chain hydrocarbons into closed chain cyclic hydrocarbons.

More specifically it is concerned with a process involving the use of special catalysts and specific conditions of operation in regard to temperature, pressure, and time of reaction whereby certain types of acetylenic hydrocarbons can be efficiently converted into aromatic hydrocarbons.

The search for catalysts to specifically control and accelerate desired conversion reactions among hydrocarbons has been attended with the usual difficulties encountered in finding catalysts for other types of reactions since there are no basic laws or rules for predicting the effectiveness of catalytic materials and the art as a whole is in a more or less empirical state. In using many catalysts even in connection with conversion reactions among pure hydrocarbons and particularly in connection with the conversion of the relatively heavy distillates and residua which are available for cracking, there is a general tendency for the decomposition reactions to proceed 0 at a very rapid rate, necessitating the use of extremely short time factors and very accurate control of temperature and pressure to avoid too extensive decomposition. {There are further difficulties encountered in maintaining the efilciency of catalysts employed in pyrolysis since there is usually a rapid deposition of carbonaceous materials on their surfaces and in their pores.

' In one specific embodiment the present invention comprises the conversion of acetylenic hydrocarbons having six or more carbon atoms in straight chain arrangement into aromatic hydrocarbons by subjecting them at elevated temperatures of the 'order of 450-700" C. to contact for definite times of the order of 01-30 seconds with catalytic materials comprising major proportions of refractory carriers of relatively low drocarbon conversion reactions which are accelerated under the preferred conditions of operaing'structural equations are introduced:

CE C CH: CH

O Hexine-l Benzene C-CH: C CH 011, 0Q. cnrcm cg an 3 0 o Under properly controlled conditions of times of contact, temperature, and pressure which obviously vary with the particular compound undergoing treatment, once-through yields of arcmatics of the order of to by weight are obtainable which can be increased to over by recycling the unconverted material. The type of reaction was unpredictable in view of the type of hydrocarbon-furnishing the starting material and the results obtained were quite unexpected. The reaction mechanisms leading to the formation of aromatics from the acetylenic hydrocarbons are probably of a complicated character since there must obviously be some shifting of the bonds betweenicarbon atoms to pro- ,duce aromatics characterized by alternate double bonds.

1 It will be seen from the foregoing that the scope of the present invention is preferably limited to the treatment of acetylenic hydrocarbons which contain at least 6 carbon atoms in straight chain arrangement. In the case of acetylene hydrocarbons containing lessthan 6 carbon atoms in linear arrangement, some formation of aromatics may take place due to primary isomerization reactions although obviously the extent of these will vary considerably with the type of compound and the conditions of operation. The process is readily applicable to acetylenesfrom. hexine up to dodecine. With increase in molecular weight beyond this point the percentage of unde'sirableside reactions tends to increase and C-OHI CHi in proportion.

The present invention is characterized by the use of a particular group of composite catalytic materials which employ as their base catalysts certainrefracto'ry oxides and silicates which-in themselves may have some slight specific cat'alytic ability in the dehydrogenation and cyclization reactions but which are improved greatly in this respect by the addition of certain promoters or secondary catalysts in minor proportions. These base supporting materials are. preferably of a rugged and reiractorycharacter capable of withstanding the severe use to'which the catalysts are put in regard to temperature during service and in regeneration by.means of air. or

other oxidizing gas mixtures after they have become fouled with carbonaceous deposits after a period of service. As examples of materials which may be employed in granular pelleted form as supports for the preferred catalytic substances may be mentioned the following;

Magnesium oxide Montmorillonite clays Aluminum oxide Kieselguhr Bauxite Crushed flrebrick Bentonite clays Crushed silica Glauconite (greensand) It should be emphasized that in the field of catalysis there have been very few rules evolved which will enable the prediction of what materials will catalyze a given reaction. Most of the catalytic work has been done on a purely empirical basis, even though at times certain groups of elements or compounds have been,

found to be more or less equivalent in accelerating certain types of reactions.

In regard to the base catalytic materials which are preferablyemployed according to the present invention, some precautions are necessary to insure that they possess proper physical and chemical characteristics before they are imp e ated with the promoters to render them more efiicient. In regard to magnesium oxide, which may be alternatively employed, this is most conveniently prepared by the calcination of the mineral mag-V nesite which is most commonly encountered in a massive or earthy variety and rarely in crystal form, the crystals being usually rhombohedral. In many natural magnesites the magnesium oxide may be replaced to the extent of several percent by iron oxide. The mineral is of quite common occurrence and readily obtainable in quantity at a reasonable figure. The pure compound begins to decompose to form the oxide at a temperature of 350 0., though the rate of decomposition only reaches a.practical value at considerably higher temperatures, usually of the order of 800 to 900 C. Magnesite is related to dolomite, the mixed carbonate of. calcium and magnesium, which latter mineral, however, is not of as good service as the relatively pure magnesite in the present instance.- Magnesium carbonate prepared by precipitation or other chemical methods may be used alternatively in place of the natural mineral. It is not necessary that the magnesite be completely converted to oxide but as a rule it is preferable that the conversion be at least over 90%, that is, so that there is less,

than 10% of the original carbonate remaining in the ignited material.

Aluminum oxide which is generally preferable as a base material for the manufacture of catalysts for the process may be obtained from natural aluminum oxide minerals or ores such as I bauxite or carbonates such asdawsonite by proper calcination, or it may be prepared by precipitation of aluminum hydrate from solutions of aluminum sulfate, nitrate, chloride, or diflerent other salts, such as alums, and dehydration of I the precipitate of aluminum hydroxide by heat. Usually it is desirable and advantageous to further treat it with air or other gases, or by other means to activate it prior to use.

' Three hydrated oxides of aluminumoccurinna- 1 ture, to wit, hydroargillite or gibbsite having the formula Alz0:.3HaO, bauxite having the formula AlzOaZHzO, and diaspore having the formula Al:0a.H-.-O.- Of these three minerals the corresponding oxides from the trihydrated and dihydrated minerals are suitable for the manufacture of the present type of catalysts and these materials have furnished types of activated alumina which are ,entirely satisfactory as supports for the preferred catalyst. Precipitated trl- N hydrates can also be dehydrated at moderately elevated temperatures to form satisfactory alumina supports. The mineral dawsonite having the formula NaaAl(C0a)s.2Al(OH)a is another mineral which may be used as a source of aluminum oxide, the calcination of this mineral giving an alkalized aluminum oxide which is apparently more eflfective as a support in that the catalyst is more easily regenerated after a period of service. Alumina in the form of powdered corimdum is not suitable as a base.

It is best practice in the final steps of preparing aluminum oxide as a base catalyst to ignite the hydrated oxides for some time at temperatures within the approximate range of coo-750 0.,

which probably does not correspond to complete dehydration of the hydroxides but apparently give a catalytic material of good strength and porosity so that it is able to resist for a long period of time the deteriorating effects of the service and 40 regeneration periods to which it is subjected. In the case of the clays which may serve as base catalytic material for supporting promoters, the better materials are those which have been acid treated to render them more siliceous. These may be pelleted or formed in any manner before or after the,addition of the promoter catalyst since ordinarily they have a high percentage of fines. The addition of certain of the promoters,

however, exerts a binding influence so that the formed materials may be employed without fear of structural deterioration in service.

Our investigations have also definitely demonstrated that the catalytic efliciency of such substances as alumina, magnesium oxide, and clays which may have some catalytic potency in themselves is greatly improved by the presence of compounds of the preferred elements in relatively minor amounts, usually of the order of less than 10% by weight of the carrier. It is most common 30 practice to utilize catalysts comprising 2 to 5% by weight of these compounds, particularly their lower oxides.

The promoters which are used in accordance with thepresent invention to produce active 5 num, tungsten and uranium. In general practically all of the compounds of the ,preferred elements will have some catalytic activity though as a rule the oxides and particularly the lower oxides are the best catalysts. Catalyst composites may be prepared by utilizing the soluble 76 from which they are absorbed by prepared'granular carriers or from which they are deposited upon the carriers by evaporation of the solvent.

The invention further comprises the use of catalyst composites made by mixing relatively insoluble compounds with carriers either inthe wet or the dry condition. In the following paragraphs some of the compounds of the elements listed above are given which are soluble in water and which may be used to add catalytic material to carriers. The known oxides of theseelements arealsolisted. a

- Chromium The. preferred catalysts in the. case of' chromium comprise essentially mixtures of major amounts of inert carriers and minor amounts of compounds of chromium such as for example, the oxides CrOz. CrOz, and particularly the sesquioxide CnOa, which results from the reduction of the two higher oxides. The oxides mentioned are particularly efllcient as catalysts for the present types of reactions but the invention is not limited to their use but may employ any of the catalytically active compounds of chromium which may be either deposited upon the carriers from aqueous or other solutions in the course of the preparation of the composites or which may be mechanically admixed therewith either in the wet or the dry condition. Such compounds as chromlc acid HaCI'Os prepared by dissolving the trioxide in water, and chromium nitrate Cr(N0a)a, are' readily soluble in water at ordinary temperatures and their solutions are therefore utilizable for adding compounds to various carriers which can be later ignited to leave a residue of the oxides which are readily reducible by hydrogen at 250? C. to form the green sesquioxide and is ordinarily reduced in the early-stage of'a run on the vapors of some paramn hydrocarbon. Alternatively, if desired, chromium hydroxides may be precipitated from aqueous solutions onto suspended particles of carriers by the use of such precipitants as the hydroxides and carbonates of the alkali metals or ammonium. Among other soluble compounds which may be added to carriers from aqueous solution may be mentioned chromium ammonium 'sulfate, chromium chlorides, chromium fluoride, chromium acetate, chromium sulfates, double salts of chromium in the alkali metals such as chromium potassium sulfate and the alkali metal salts of the various acids of chromium.

Molybdenum examples of such soluble compounds may be men-' tioned molybdenum pentachloride in hydrochloric acid solution, molybdic oxide dissolved in aqueous ammonia or nitric acid and ammonium molybdate. Other soluble compounds are the tetra bromide, the oxychloride, andthe basic thiocyanate. Compounds of molybdenum which are insoluble'in water or other ordinary solvents may be mixed mechanically with the alumina either in the dry or moist condition.

3 Tungsten Oxides ditungsteu. such as the sesquioxide W203- and the dioxide W0: which result from the reduction of the trioxide W0: are particularly eiliclent as catalysts for the present types of reactions, though the invention is not limited to their use but may employ other compounds of tungsten. Tungsten trioxide dissolves readily in' aqueous ammonia solutions and may thus be conveniently used as an ultimate source of tungstic acids, which correspond to various degrees of hydration of the trioxide and which may be ignited to form the trioxide. Alternately the tungstic acids may be precipitated from solutions in water by the use of ammonium oral- .kali metal hydroxides or carbonates as precipitants,-the hydroxide being later ignited to form mixtures of the trioxide and the dioxide, which may undergo reduction by hydrogen or the gases and vapors in contact with the catalyst in the normal operation of the process.

Uranium In regard to uranium, which is the heaviest member of the present natural group of elements whose compounds arcpreferred as catalysts, it may merely be stated that while this element furnishes catalytic compounds havin a relatively high orderof activity, its scarcity and cost naturally precludes its extensive use!!! practice. Uranium shows a series of oxides in cluding'the dioxide U02, a trioxide U03, a hydr'ated peroxide 110421-120 and an oxide U300 characteristic of pitchblende. Any of these'oxides may be used as catalysts as well as some of the other compounds of this element.

The most general method for adding promoting materials to the preferred base catalysts, which if properly prepared have a high adsorptive capacity, is to stir the prepared granules of from approximately 4 to mesh into solutions of salts which will yield the desired promoting compounds on ignition under suitable conditions. In some instances the granules may be merely stirred in slightly warm solutions of relatively low solubility it may be necessary to add thesolution in successive portions to the adsorbent base catalyst with intermediate heating to drive ofi solvent in order to get the required quantity of promoter deposited uponthe surface and in the pores of the base catalyst. The temperatures used for drying and calcining after the addition of the promoters from solutions will depend entirely upon the individual characteristics of the compound added and so general ranges of temperature can be given for this step.

In some instances promoters may be deposited from solution by the addition of precipitants which cause the deposition of precipitates upon the catalyst granules. As a rule methods of mechanical mixing are not preferable, though in some instances in the case of hydrated or readily fusible compounds these may be mixed with the proper proportions of base catalysts and uniformly distributed during the condition of fusing or fluxing. I

In regard to the relative proportions of base catalyst and promoting materials it may be stated in general that the latter are generally less than 10% by weight of the total composites.

:The effect upon the catalytic activity-of the base catalysts .caused by varying the percentage of any given compound or mixture of compounds deposited thereon is not a matter for exact calcuiation but more one for determination by ex- .periment. Frequently good increases in catalytic effectiveness are obtainable by the deposition of as low as 1% or 2% of a promoting compoundupon the surface and in. the pores of the base catalyst, though the general average is about 5%.

employed with acetylenic hydrocarbons having from 6-12 carbon atoms to the molecule are of the order of 5 to 20 seconds. It will be appreciated by those familiar with the art of hydrocarbon conversion in the presence of catalysts that the factors of temperature, pressure, and time will frequently have to be adjusted from the results of preliminary experiments to produce the best results in any given instance. The criterion of the yield of an aromatic having the same number of carbon atoms in the ring as the original acetylenic hydrocarbon charged had in the chain will serve to fix the best conditions of operation. In a general sense, the relations between time, temperature, and pressure are preferably adjusted so that rather intensive conditions are employed of sufficient severity to insure a maximum amount of the desired cyclizaside reactions.

In operating the process the general procedure is to vaporize hydrocarbons or mixtures of hydrocarbons and after heating the vapors to a suitable temperature within the ranges previously specified, to pass them through stationary masses of granular catalytic material in vertical cylindrical treating columns or banks of catalyst-containing tubes in parallel connection.

' Since the reactions are endothermic it may be necessary to apply some heat externally to maintain the best reaction temperature. After passing through the catalytic zone the products are submitted to fractionation to recover cuts or fractions containing the desired aromatic product with the separation of fixed gases, unconverted hydrocarbons and heavier residual materials, which may be disposed of in any suitable manner depending upon their composition. The overall yield of aromatics may be increased by recycling the unconverted acetylenic hydrocarbons to further treatment with fresh material, although this is a more or less obvious expedient and not specifically characteristic of the present invention.

The present types of catalysts owing to their more or less specific action under the limited conditions of operation specified maintain their activity' over relatively long periods of time. However, when their activity begins to diminish after a period of service, it is readily regenerated other oxidizing gas at a moderately elevated temperature, usually within'the range employed in the dehydrogenation and cyclization reactions. This oxidation effectively removes traces of carbon deposits which contaminate; the surface of the particles anddecrease their efliciency. It is characteristic of the present types of catalysts that they may be repeatedly regenerated with only a'very gradual loss of catalytic efilciency.

During oxidation with air or other oxidizing gas mixture in regenerating partly spent .material, there is evidence to indicate that when the lower oxides are employed, they are to a large extent, if not completely, oxidized to higher oxides which combine with basic carriers to form compounds of variable composition. Later these compounds are decomposed by contact with reducing gases in the first stages of service to reform the lower oxides and regenerate the real catalyst and hence the catalytic activity.

Emmple I Hexine-l was vaporized and passed over a granular catalyst comprising an alumina base supporting about 4%by weight of chromium sesquioxide, using a'temperature of 530 0., substantially atmospheric pressure; and atime of contact of 19 seconds. The yield of pure benzene in a single pass under these conditions was found to be 24% by weight of the hexine-l charged.-

By proper fractionation of products and recycling of the unconverted material the ultim e yield of benzene was finally raised to 49%.

Example II Espample III Hexine-l was vaporized and passed over a granular catalyst comprising an alumina base supporting a minor proportion. by weight of molybdenum sesquioxide. The yield of pure benzene in a single pass under these conditions was found to be 24% by weight of the normal hexine-l charged. By proper fractionation of products and recycling of the unconverted material the ultimate yield of benzene was finally raised to 67%.

The general procedure in the manufacture of the catalyst was to dissolve ammonium molybdate in concentrated ammonia and utilize this solution as a means of .adding molybdenum oxides to a carrier. 20 parts by weightof ammonium molybdate was dissolved in about 50 parts by weight of concentrated aqueous ammonia and the solution then diluted by the addition of approximately one equal volume of water. The solution was then added to about 250 parts by weight of activated alumina which had been pro- .duced by calcining bauxite at a temperature of about 700 C; followed by grinding and sizing to produce particles of approximately 8-12 mesh. Using the proportions stated the alumina exactly absorbed the solution and the particles were first dried at 100 C. for about two hours and. the temperature was then raised to 350 C. in a period of eight hours. After this calcining treatment the particles were placed in a reaction chamber and the molybdenum oxides reduced in a current of hydrogen at about 500 0., when they were then ready forservice.

The vapors of the hexine-l were passed over the catalyst at a temperature of 530 C. and substantially atmospheric pressure, using a rate which corresponded to a time of contact of about 17 seconds. The yield of pure benzene under these conditions was found to be 23% by weight of the normal hexine-l charged. By recycling of the unconverted material the ultimate yield of benzene was raised to 46%.

Example IV The procedure in the manufacture of the catalyst was to dissolveammonium tungstate in water and utilize this solution as a means of adding tungsten oxides to a carrier. 15 parts by weight of ammonium tungstate was dissolved in about parts by weight of water and the solution was then added to about 250 parts by weight of activated alumina which had been produced by calcining bauxite at a temperature of about 700 0., followed by grinding and sizing to produce particles of approximately 8-12 mesh. Using the proportions stated the alumina exactly absorbed the solution and the particles were first dried at 100- C. for about two hours and the temperature was then raised to 350 C. in a period of eight hours. After this calcining treatment the particles were placed in a reaction chamber and the tungsten oxides reduced in a current of hydrogen at about 500 0., when they were the ready for service.

Hexine-l was vaporized and passed over the granular catalyst using a temperature of 530 C., substantially atmospheric pressure, and a time of 17 seconds. The yield of pure benzene under these conditions was found to be 16% by weight of the normal hexine-l charged. By recycling of the unconverted material the ultimate yield of benzene was raised to 48%.

We claim as our invention:

1. A process for the production of aromatic hydrocarbons from acetylene hydrocarbons having at least 6 carbon atoms in straight-chain arrangement, which comprises dehydrogenating and cyclicizing the acetylene hydrocarbon by subjection to a temperature of the order of 450 to 700 C. for a period of about 0.1 to 30 seconds in the presence of a compoundof a metal from the lefthand column of Group VI of the periodic table and selected from the class consisting of chromium, molybdenum, tungsten and uranium.

2. A process for the production of aromatic hydrocarbons from acetylene hydrocarbons having at least 6 carbon atoms in straight-chain arrangement, which comprises dehydrogenating and cyclicizing the acetylene hydrocarbon by subjection to a temperature of the order of 450 to 700 C. for a period of about 0.1 to 30 seconds in the presence of an oxide of a metal from the lefthand column 0! Group VI of the periodic table and selected from the class consisting of chromium, molybdenum, tungsten and uranium.

3. A process for the production of aromatic hydrocarbons from acetylene hydrocarbons having at least 6 carbon atoms in straight-chain arrangement, which comprises dehydrogenating and cyclicizing the acetylene hydrocarbon by subjection to a temperature of the order of 450 to 700 C. for a period of about 0.1 to 30 seconds in the presence of a solid granular catalyst comprising a major proportion of a carrier of relatively low catalytic activity supporting a minor proportion of a compound of a metal from the lefthand column of Group VI of the periodic table and selected from the class consisting of chromium, molybdenum, tungsten and uranium.

4. A process for the production of aromatic hydrocarbons from acetylene hydrocarbons having at least 6 carbon atoms in straight-chain arrangement, which comprises dehydrogenating and cyclicizing the acetylene hydrocarbon by subjection to a temperature of the order of 450 to 700 C. for a period of about 0.1 to 30 seconds in the presence of a solid granular catalyst comprising a major proportion of a carrier of relatively low catalytic activity supporting a minor proportion 01 an oxide of a metal from the lefthand column of Group VI of the-periodic table and selected from the class consisting of chromium, molybdenum, tungsten and uranium.

5. A process for the production of aromatic hydrocarbons from acetylene hydrocarbons having at least 6 carbon atoms in straight-chain arrangement, which comprises dehydrogenating and cyclicizing the acetylene hydrocarbon by subjection to a temperature of the order of 450 Y to 700 C. for a period of about 0.1 to 30 seconds inthe presence of aluminum oxide supporting a relatively small amount of a compound of a metal from. the lefthand columnof Group VI 01 the periodic table and selected from the class consisting of chromium, molybdenum, tungsten and uranium.

6. A process for the production of aromatic hydrocarbons from acetylene hydrocarbons having at least 6 carbon atoms in straight-chain arrangement, which comprises dehydrogenating and cyclicizing the acetylene hydrocarbon by subjection to a temperature of the order of 450 to 700? C. for a period of about 0.1 to 30 seconds in the presence of aluminum oxide supporting a relatively small amount'of an oxide of a metal from the lefthand column of Group VI .of the periodic table and selected from the class consisting of chromium, molybdenum, tungsten and uranium.

. ARIS'IID V.. GROSSE. WILLIAM J. MA'I'IOX. 

